LONDON -- There was a Galápagos fern, collected by Charles Darwin himself. There were mahogany cabinets filled with plants from the East India Company, including the two tea leaves whose discovery launched the Indian tea trade. There was an antelope net made of baobab bark, from David Livingstone's storied Zambezi expedition more than 150 years ago.
The public rarely gets to see these treasures. Along with more than seven million preserved plant specimens, they are hidden away in the Herbarium of Kew Gardens, which sits largely unnoticed beside the sprawling botanic garden that attracts a million visitors each year. The herbarium, visited each week by scores of researchers from around the world, is usually closed to tourists.
But on a recent autumn weekend, its gates swung open. It was among hundreds of buildings -- from a decommissioned power station to 10 Downing Street -- participating in Open House London, an annual citywide architectural event that casts light on typically private spaces.
At Kew, more than 400 people -- some of them passionate gardeners, some casual visitors -- grabbed the chance to peek inside.
The tours centered on the herbarium's original wing, built in 1877. A soaring rectangular warehouse with three open levels along its sides braced by red iron columns, it resembles an old-fashioned penitentiary -- what employees affectionately call "jailhouse style."
Dozens of cabinets on each floor point to the center of the room, creating small "cells" between the stacks. Enormous windows flood the space with light, a 19th-century effort to minimize the number of gas lanterns in a place filled with paper.
And it is the paper itself, musty and old, thousands of pages holding stalks and buds from around the world, that overwhelms visitors when they enter the herbarium.
"Oh, the smell," Kathleen Haughney of London said as she walked through the doorway. It is as if the spine on a book untouched for hundreds of years has been cracked.
She and her husband were waiting when the gates opened. Interested in both horticulture and architecture, they had come to see what science lay inside the herbarium.
"It's a chance to see what you generally cannot," she said.
Admiring the beautifully precise sketches made by John Kirk on the Livingstone expedition, Petra Broddle, an assistant botanist who helped lead the tours, urged visitors to imagine their journey more than 150 years ago from Central Africa to Kew.
"Canoes overturned, things were lost, Kirk almost drowned, but this is here," she said, sweeping her hand above the table. "That is hard-core traveling these specimens have done to get here."
Catherine Maher, a writer and teacher from Shropshire, marveled at the scope of the collection, much of it assembled when the British Empire stretched around the world.
"The idea that they've got all this stuff is incredible," she said. "The Victorians were just mad. They just went round the world nicking all they could. But in a way, thank goodness they did."
One wooden table held two boxes of giant curled palms collected in the Amazon by Alfred Russel Wallace, the Welsh naturalist and a contemporary of Darwin. Next to them was a field guide Wallace wrote about palms after the expedition, placed there by David Goyder, the herbarium botanist who chose the items for the open house.
Alongside that display were current guides to wild plants in Oman and the flora of Thailand. Stacks of recently collected samples from Mozambique stood beside the specimens from the Livingstone expedition.
Dr. Goyder took care to emphasize the links between past and present science, the herbarium's support for conservation efforts around the world, and the discoveries of new plants by its own staff. He noted that the herbarium receives about 30,000 specimens each year for identification and study.
Staff members work at desks stationed among the cabinets, and Dr. Goyder pointed out his own.
"Welcome to my office," he said. "We don't want to give the impression that we're a museum. We are a living research institution."
Soon after the open house, Dr. Goyder left for a monthlong research trip to the mountains of southwestern Angola. Another researcher helping with the tours, Andre Schuiteman, plans to travel to southeastern Asia this fall to find orchids.
And despite the new technology each will take -- GPS devices, cameras rather than pencils and watercolors -- much of what they do remains rooted in the past.
"We still look at plants stuck to a piece of paper," Mr. Schuiteman told the visitors. "We still go to faraway places and collect samples. We keep up with our times, but we also still keep to the 19th century in some ways."
It was this continuity that struck Jo Milano, 31, a masseuse from Brighton who had arrived not knowing what to expect.
"I looked around and it was like a museum, all those plants like a historic exhibit, but it's actually still very current," she said.
"These are scientists who are still working on what's been started so long ago. When you think of the work that's gone on in collecting and storing and still does, it's amazing."
This article originally appeared in The New York Times. First Published October 16, 2013 2:01 PM